From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 57BBD1E52C; Wed, 2 Oct 2024 14:21:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1727878879; cv=none; b=TNScBAlZv5+Hav92spKNmNDELW0nC3vsPff2AIFdr4SOsmmgs2Wl4lSGILy+tmCdOozOqUzykvqhaThkL/Jwh8CKX7Mp2ZLJhnt0BRoxA3ZfPq3xoJ64UKjWjzJJUtPbbKlxDFSqJfBBSBKO45HBqJiVOtUuWLnoGRyBbz7JZKg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1727878879; c=relaxed/simple; bh=hUfEkIWzE0QnqZTsR/uzzE37+T2PASmyMZfHfZxjkS4=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=cHCcAznWz57gig1IgoP3EQlZRCTSYaWi5q+gDbB+61ooBZTebxM5qyZgvlEbkFfljiqZZ9Gnm0WPYeDVmox2CN6BKPB042t1Whj7t57vFNGZyC5ZMtgck4nLFjEh5Fwo3K51JvsBCq/pI2d4ospgkuHHeg1+ARFZYGX0ky1abW4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=oxr086wt; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="oxr086wt" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A9B0AC4CECE; Wed, 2 Oct 2024 14:21:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1727878879; bh=hUfEkIWzE0QnqZTsR/uzzE37+T2PASmyMZfHfZxjkS4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=oxr086wt0DzCrhYEP/fs+VU5uaMnnwDkeqA/Fz7j8E//FTlHFPNfZf6kxPSnzWeTR WaUBFnSY+LZg6ri6dUYSJgybHWvaWfngCUKD7CseC8iPCVuHSmrI2pPuMK63BjZK41 2JEfrsMCySIfwQzkXhmDtYEEGuw5DVq/DYmiyWk8= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Jann Horn , Chao Yu , Eric Biggers , Jaegeuk Kim Subject: [PATCH 6.10 563/634] f2fs: Require FMODE_WRITE for atomic write ioctls Date: Wed, 2 Oct 2024 15:01:03 +0200 Message-ID: <20241002125833.338557387@linuxfoundation.org> X-Mailer: git-send-email 2.46.2 In-Reply-To: <20241002125811.070689334@linuxfoundation.org> References: <20241002125811.070689334@linuxfoundation.org> User-Agent: quilt/0.67 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.10-stable review patch. If anyone has any objections, please let me know. ------------------ From: Jann Horn commit 4f5a100f87f32cb65d4bb1ad282a08c92f6f591e upstream. The F2FS ioctls for starting and committing atomic writes check for inode_owner_or_capable(), but this does not give LSMs like SELinux or Landlock an opportunity to deny the write access - if the caller's FSUID matches the inode's UID, inode_owner_or_capable() immediately returns true. There are scenarios where LSMs want to deny a process the ability to write particular files, even files that the FSUID of the process owns; but this can currently partially be bypassed using atomic write ioctls in two ways: - F2FS_IOC_START_ATOMIC_REPLACE + F2FS_IOC_COMMIT_ATOMIC_WRITE can truncate an inode to size 0 - F2FS_IOC_START_ATOMIC_WRITE + F2FS_IOC_ABORT_ATOMIC_WRITE can revert changes another process concurrently made to a file Fix it by requiring FMODE_WRITE for these operations, just like for F2FS_IOC_MOVE_RANGE. Since any legitimate caller should only be using these ioctls when intending to write into the file, that seems unlikely to break anything. Fixes: 88b88a667971 ("f2fs: support atomic writes") Cc: stable@vger.kernel.org Signed-off-by: Jann Horn Reviewed-by: Chao Yu Reviewed-by: Eric Biggers Signed-off-by: Jaegeuk Kim Signed-off-by: Greg Kroah-Hartman --- fs/f2fs/file.c | 9 +++++++++ 1 file changed, 9 insertions(+) --- a/fs/f2fs/file.c +++ b/fs/f2fs/file.c @@ -2123,6 +2123,9 @@ static int f2fs_ioc_start_atomic_write(s loff_t isize; int ret; + if (!(filp->f_mode & FMODE_WRITE)) + return -EBADF; + if (!inode_owner_or_capable(idmap, inode)) return -EACCES; @@ -2230,6 +2233,9 @@ static int f2fs_ioc_commit_atomic_write( struct mnt_idmap *idmap = file_mnt_idmap(filp); int ret; + if (!(filp->f_mode & FMODE_WRITE)) + return -EBADF; + if (!inode_owner_or_capable(idmap, inode)) return -EACCES; @@ -2262,6 +2268,9 @@ static int f2fs_ioc_abort_atomic_write(s struct mnt_idmap *idmap = file_mnt_idmap(filp); int ret; + if (!(filp->f_mode & FMODE_WRITE)) + return -EBADF; + if (!inode_owner_or_capable(idmap, inode)) return -EACCES;